Broadly defined, the proposed project centers on the relationship between language and cognition, focusing on the consequences of bilingualism for cognitive, linguistic, and developmental processes. The objective of the present work is to understand how using more than one language changes cognitive architecture and impacts general cognitive function. Our previous research demonstrates that auditory input co-activates both languages in parallel during bilingual spoken comprehension via bottom-up cascading activation. Using an interactive activation framework, the proposed project further advances understanding of bilingual spoken language processing by examining the role of top-down activation and the interaction of top- down, bottom-up, and lateral activation during bilingual spoken language comprehension. Four studies utilize eye-movements and other behavioral measures to examine how bilinguals manage co-activation and interaction across the two languages, across modalities (e.g., between spoken and sign languages), across levels (e.g., between segmental and suprasegmental input), and in sentence context. The proposed research also examines cognitive consequences of bilingualism by establishing a direct link between cross-linguistic co- activation and inhibitory control. Theoretically, the proposed research contributes to understanding the complex relationship between language and cognition from the unique vantage point of bilingualism and specifies the interactive nature of top-down, bottom-up and lateral activation in the bilingual cognitive architecture. Addressing broader societal needs, this work has practical implications for the large segment of the American population who speaks a language other than English at home and for whom clinical and educational outcomes can be improved by capitalizing on the interaction and co-activation of two languages.